The evolution of the electronics industry in recent years has resulted in a steady decrease of integrated circuit feature sizes. With the introduction of the 256K chip and research on the 512K chip in progress, feature sizes are shrinking to such a degree that many of the traditional semiconductor processing techniques are no longer adequate. Until recently, doped polysilicon has been used extensively as a conductor for gates and gate interconnects on metal-oxide semiconductor (MOS) devices. Doped polysilicon was chosen because it can withstand subsequent high temperture processing steps and because it has electrical properties, such as a bulk resistivity of about 1,000 .mu..OMEGA.-cm, which are desirable. As conductor line widths are reduced to below 2.mu., however, the resistance of polysilicon conductive lines is large enough to degrade the high speed performance of devices. Thus, with minimum feature sizes of 1.mu. or less, the electronics industry has looked to refractory metal silicides as a solution to gate and gate interconnect problems in high density chip production.
Refractory metal silicides are now being used in place of polysilicon or in addition to polysilicon (as a two layer polysilicon-silicide conductor sometimes referred to as a polycide). Refractory metal silicides have very low bulk resistivities (approx. 15-100 .mu..OMEGA.-cm), can withstand temperatures in excess of 1,000.degree. C. and, in general, do not oxidize easily. The silicides commonly associated with the formation of gate interconnects are titanium silicide (TiSi.sub.2), tungsten silicide (WSi.sub.2), molybdenum silicide (MoSi.sub.2) and tantalum silicide (TaSi.sub.2).
The term metal silicide as used herein is defined as a metallic compound having the general formula M.sub.x Si.sub.y where M=a metal, 0&gt;x.gtoreq.1 and 0&gt;y.gtoreq.1.
Currently, a variety of methods are employed to produce conductive silicide coatings. They include sputtering or co-sputtering techniques, evaporation or co-evaporation processes, chemical vapor deposition processes requiring high substrate temperatures (pre- or post-deposition), and plasma induced chemical vapor deposition. For a detailed discussion of many of these methods see Murarka, Refractory Silicides for VSLI Production, Academic Press, 1983, pp. 115-31. All of these processes require high capital expeditures and considerable maintenance expenses in order to be effectively operated. In addition to the economic drawbacks, these processes are difficult to control and, therefore, the reproducability of chemically consistent products is a significant problem.
We have discovered a process for forming conductive films comprising metal silicides which is simple and easily monitored (in terms of coating thickness, step coverage, etc.), requires low capital expenditures and yields chemically consistent products. That process is disclosed in U.S. Pat. No. 4,617,237, filed concurrently herewith, entitled "PRODUCTION OF CONDUCTIVE METAL SILICIDE FILMS FROM ULTRAFINE POWDERS", the disclosure of which is hereby incorporated by reference.
Metal compound powders are ordinarily produced by grinding, ball milling or jet milling (e.g., fluid energy milling). These processes are capable of producing finely-divided powders with average particle sizes (diameters) of about 0.1 to 2.50 microns. However, it is not possible to obtain uniformly sized ultrafine particles by employing these processes.
Finely divided powders have been produced in recent years by more sophisticated techniques such as plasma gas heating. See, for example, U.S. Pat. No. 4,022,872. Such processes employ gas phase reactants which are brought together within a reactor and heated by hot plasma gas to the proper reaction temperature. The powders produced by such processes, typically, are at least 90% composed of powders rnging in size between 0.05 and 1.0 micron.
Ultrafine powders are defined as powders having an axial dimension (i.e., a dimension taken along any axis passing through a particle of the powder) of less than about 2000 .ANG.. Such powders have recently been produced by laser induced gas phase reactions. See, for example, Danforth et al., "Synthesis of Ceramic Powders by Laser Driven Reactions" Industrial Liaison Program Report No. 10-17-82, ILP Publications Office, M.I.T., Cambridge, MA. In fact, powders produced by this process are generally less than 500 .ANG. in diameter and spherical.
We have discovered that certain gas phase reactants can be exposed to high intensity light to produce ultrafine powder comprising metal silicide and free silicon. This ultrafine powder is particularly suited for use in our film making process because the powders form stable suspensions and because the powder composition produces a highly conductive strongly adherent layer after firing.